A compressor, which is a driven fluid machine that converts low-pressure air into high-pressure air, is the heart of a cooling system. It sucks low-temperature and low-pressure coolant air from an air sucking pipe, compresses the coolant air using a piston driven by an electric motor, and discharges high-temperature and high-pressure coolant air to an air discharging pipe, thereby providing driving power for a cooling cycle and realizing the cooling cycle including compression→condensing (heat radiating)→expanding→evaporating (heat absorbing) steps.
Linear compressors are widely used in small cooling output fields such as refrigerators, and have the advantages of simple structures, less frictional losses, low noise, convenient adjustment of flow rates by adjusting the voltages, enhanced simplicity and reliability compared with frequency converting adjustments and application of lubricants including less or no grease. For example, the Chinese patent CN 203394701U discloses a linear compressor. As shown in FIG. 1, the linear compressor includes an air discharging mechanism 1 and a compressor assembly. The compressor assembly includes a cylinder 16, a piston assembly, a movable-magnet type linear oscillating motor, a resonance spring 8 and a compressor housing. The piston assembly includes a piston 2, a piston rod 3, a rod end plate 10 and an air sucking valve 15. The air discharging mechanism 1 includes an air discharging valve sheet 17, and an air discharging valve plate 18 etc.
The working process of the linear compressor is electronically controlled. When the output power is relatively small, as the stroke of the piston 2 of the linear compressor is relatively small, the piston 2 can easily collide with the air discharging valve plate 18, causing failure of the compressor. Thus, when designing the frequency converting board of a linear compressor, a protection program will be set to prevent damages to the mechanical members of the compressor. For example, the frequency converting board of the linear compressor will activate the protection program to stop the linear compressor.
When a refrigerator works at low temperatures, the thermal load of the refrigerator is relatively low, and the cooling output required by the compartments is relatively low. At this time, the linear compressor will operate at a relatively low output power. As a result, the stroke of the piston of the linear compressor is relatively small, and there is a risk of collision between the piston and the air discharging valve plate.